a. Field of the Invention
The invention is in the field of fluid handling apparatus having a plurality of inputs of varying characteristics that converge at a common zone.
b. Description of the Related Art
Corrosion is a major cause of failure of pilings and other structural members in marine environments. Cathodic protection greatly reduces corrosion where pilings are constantly in contact with water, but is of little help in the areas where alternate exposure to air and water occurs due to tidal effects and to wave action. It has been found that encapsulating the piles with plastic formulations will greatly reduce corrosion in this area of piles. This encapsulation process is described in U.S. Pat. Nos. 4,876,896 and 4,993,876, which description is incorporated by reference herein. One type of plastic formulation which provides an exceptionally strong and abrasion-resistant coating for piles is an epoxy resin blended with silica sand. In application, a liquid resin-sand mixture and a liquid hardener-sand mixture are pumped through a static mixer and into a form surrounding a pile. The resulting polymer-sand mixture fills the void between the form and the pile and then hardens. This hardened polymer-sand mixture binds to both the form and the pile.
A critical piece of equipment in this encapsulation process is the pump used to inject the resin-sand mixture and the hardener-sand mixture into the static mixer and thence into the form. Since the weight ratio of sand-free hardener to sand-free resin is an important factor in achieving the desired physical properties of the polymer, it is essential that the volumetric flows of said hardener and said resin monomer be maintained to achieve the proper weight ratio of said hardener to said resin. Additionally, as both the hardener mixture and the resin mixture contain silica sand, the effective viscosity of each of the sand-free monomers is increased by the addition of such aggregate and must be taken into account in the pumping process. Minor changes in the volume ratio of hardener to resin monomer, such as that caused by small temperature changes which affect the densities of the mixtures, do not seriously affect the physical properties of the final polymer and are ordinarily ignored. While many formulations use a ratio of resin to hardener of 1:1, other ratios can be accommodated by adjusting the diameters of the piston pump cylinders.
In practice, plural component pumping systems employ piston pumps to pump the said mixtures into the static mixer and thence into the form, although diaphragm pumps or progressive cavity pumps could theoretically be employed. However, these other types of pump have not usually been employed because of problems with maintenance or with timely detection of the need for maintenance. In order to keep the ratio of the flows of said hardener and said resin constant, two pumps are used in practice, each being driven by its own drive mechanism controlled by a timing device or both being driven by a single driving mechanism. Since the viscosities of the hardener-sand mixture and the resin-sand mixture can vary considerably, both with temperature and with the concentration of sand in the mixtures, the backpressures on the two pumps will ordinarily be different, resulting, in the case of a single drive mechanism, in unequal forces on the pistons of the two said pumps with resulting torque on the driving mechanism and on the aforesaid pumps. This torque tends to distort the pumps, leading to non-uniform wear on the pump pistons and cylinders.
The presence of sand in the aforesaid pump feeds produces a very abrasive medium, which causes severe wear on all parts of the pump with which the sand comes in contact. This wear results in pump leaks, which cause an unacceptable imbalance in the ratio of the feeds of hardener-sand mixture and resin-sand mixture, necessitating replacement of worn parts before operation can be continued. Typical throughput of pumps before such maintenance is required is 4.25-5.66 cubic meters (150-200 cubic feet) of material for pumps presently being used in this service. If it becomes necessary to shut down a pump for repairs during the filling of a form, it is necessary to return the pump to service quickly, as the polymer-sand mixture has a pot life of approximately one hour or less. Pumps currently in use require several hours to repair, and an interrupted injection of encapsulating feed will result in either beginning a second injection cycle, with the risk of an unacceptable “cold” joint between the two injections, or abandonment of the first injection, followed by removal of the partial injection, re-cleaning the pile, replacing the form, and injecting with the polymer-sand mixture once again.
The silica sand, having more than twice the density of either the said resin or the said hardener, tends to settle out and concentrate in the bottoms of the respective pump feed tanks and to settle in pumping lines at low flow rates. Even at normal flow rates some settling is found to occur in any region of the pipeline or other part of the pumping system where enlargements or non-uniform cavities exist. Such concentration in the feed tanks will alter the composition of the mix being fed to the molds and therefore can cause non-uniform physical properties in the coating on the piles being encapsulated. In order to avoid such non-uniformity, it has been found necessary to adequately stir the mixtures in the respective pump feed tanks. The mixing action in the feed tanks must be adequate to suspend the sand in the respective liquid media and also to avoid entraining air into the liquid. Air bubbles or foam entrained in the liquid will expand during the suction stroke of the piston pump and thereby prevent the complete filling of the pump cylinder, thus altering the volume of liquid discharge on the pressure stroke.
In the practical application of coatings to marine pilings the pumping unit is located as close to the pile as is convenient in order to minimize the length of line through which the mixtures must be transferred. Consequently, it is advantageous that the pumping unit be portable and compact. The resin and the hardener are normally supplied in 19 liter (5 gallon) cans and the sand is supplied in 23 kg (50 pound bags). All ingredients are normally fed manually into the feed tanks, and it is most convenient to avoid having to lift the materials onto a platform before feeding them into the respective feed tanks. Ergonomic considerations dictate that these feed materials not be lifted above chest height while charging them into the feed tanks, thereby limiting the height of the pumping unit. Existing pumping units do not meet all of these criteria.
Many of the moving parts of existing pumping units are exposed. Workers can come into contact with, and suffer injury from, components such as piston pumps, drive pumps, and mixing paddles. As mentioned above, injury can also result when workers have to repeatedly lift 19 liter (5 gallon) monomer cans and 23 kg (50 pound) bags of sand onto the elevated platforms of existing pumping units.
Maintenance of existing pumps requires a minimum of four hours to disconnect feed and discharge lines from the pump, to remove the pump from the unit and dismantle it, to replace worn parts, to reinstall the pump and to reconnect the piping. Such work done in the field normally requires additional time because of the lack of efficient repair facilities. With the aforementioned frequency of required repairs, much time is expended in maintenance, resulting in a significant loss of time in productive work.
The resin monomer normally used in this application is white in color, and the hardener monomer normally used in this application is black in color. A combination of the two components in the proper ratio results in a particular shade of gray. To ensure the proper mixing of the two components, it is necessary to monitor the color of the polymer-sand mixture during the pumping process. This is customarily accomplished by a diver observing the color and progression of the polymer-sand mixture through the translucent form as said mixture fills the void between the form and the structural member. This approach is problematic, however, since it is critical for the diver to know the composition of the polymer-sand mixture before it is pumped into the form. Further, in low-visibility conditions, it becomes difficult for the diver to see the exact shade of the polymer-sand mixture though the translucent form.
Oftentimes, the two monomers are not sufficiently blended, which results in poor adhesion to the form and/or the structural member that is intended to be protected. The current practice to increase the mixing characteristics of the static mixer is to utilize a second standard-sized static mixer in line with the first. This invariably results in significantly increased backpressure on the system. Standard static mixers are likewise prone to blockage by foreign material or unmixed aggregate due to their small diameter. Cleaning standard static mixers is accomplished by removing the mixing element from the housing, and as this is often done after the polymer-sand mixture has begun to cure, the process can be difficult.
What is needed, therefore, is an apparatus for pumping and mixing high aggregate plural components of differing viscosities that does not cause unequal forces between the pumps, is more resistant to wear, reduces settling of aggregate, is quick to repair, does not require lifting bags and buckets greater than chest height, is compact, has reduced backpressure, and permits the operator to verify proper mixture amounts and proper blending before the mixture is poured.